EFFECT OF COMPLEX FORMAT ION ON ELECTROCHEMICAL BEHAVIOUR OF METAL-CONT AINING WASTE WATERS

Abstract

The problem of preventing the heavy metals and other toxic substances release in environment due to the discharges of untreated plating and rinsing solutions is actual from both ecologic and economic point of view. It is crucial to prevent the environmental pollution and uncontrolled losses of resources (metals and other substances). The treatment technologies used today are not always efficient and cost saving and in some cases they may even provoke the secondary pollution of environment. Electrochemical treatment of industrial waste waters is one of the most promising technologies as it implies the same principles as the main technological processes and does not require introducing of chemicals into the trea ted solution. However, until now this method was given insufficient attention, although there are ce rtain publications in this field [1]. The electrochemical behaviour of some d- metal complexes was studied and discussed from the viewpoint of water treatment requirements. The studies performed in th e model plating solutions of Zn, Ni, Cu ammonia and pyrophosphate complexes, polynuclear Cr complexes have shown that the application of conventional reagent waste water treatment methods for such solutions would be inefficient. Examination of potentio-dynamic polarization curves registered in studied solutions have s hown, that due to the formation of series of Zn ammonia complexes, alkaline treatment will not ensure Zn removal from such solutions, and application of electrocoagulation treatment method will not be efficient enough. It was also found that in case of Ni-, Cr- containing solutions electrochemical treatment can be used for Cu removal, whereas for the effective Cr(VI) removal the electrocoagulation would be required, which entails the redox processes resulted in the formation of hydroxides. The research has shown that the approach on the heavy metal removal from the used plating solutions may be different depending on the plating bath composition.